One of the most difficult problems in cleaning automotive bodies prior to the finishing steps leading to the application of automotive paint is in the removal of unwanted sealants commonly used in sealing and waterproofing joints and openings between metal parts. When such sealants are applied, usually by means of extrusion through grease guns, excess quantities of sealant are often inadvertently extruded or dripped onto the adjacent metal parts. Frequently, dust or other undesirable material settles on and adheres to this sealant. The excess sealant must be removed from the metal before the application of a conversion coating prior to painting.
The sealants commonly used in the automotive and allied industries are compositions containing a resin such as an epoxy resin or a vinyl resin, e.g. polyvinyl chloride resin; a heavy blending oil such as linseed oil, dioctylphthalate, diethylphthalate, dibutylphthalate, etc.; a fixotrope, e.g. CARBOSIL; and a filler such as calcium carbonate or limestone. Such sealants are of course water-insoluble, since their purpose and use as sealants is to seal and waterproof the joints and openings in which they are used. These sealants are also used in allied industries, such as the aviation industry, in the manufacture of trucks and buses, and in the manufacture of tractors and other motorized farm equipment.
One method for removing such unwanted sealants is by the use of kerosene. However, kerosene has many disadvantages, including toxicity to the workers using it on prolonged exposure; flammability problems; unpleasant odor; and the problem of removing excess kerosene from the metal parts, since kerosene has low water solubility and cannot be readily removed by use of a water rinse. In fact, when automotive bodies containing areas coated with kerosene are immersed or sprayed one after the other in a standard cleaning solution prior to the application of a conversion coating to the metal bodies, the bath becomes contaminated relatively rapidly and rendered ineffective by the kerosene, requiring frequent down time and expense in draining the kerosene-contaminated bath and making up a fresh bath. The use of emulsifiable kerosene was an improvement but did not satisfactorily eliminate the above problems. Hence, until commercially alternative means were developed for removing the sealant the use of kerosene had to be tolerated.
Aqueous detergent compositions have been developed to remove the undesirable sealant and these compositions are now replacing kerosene. Such compositions have been disclosed and claimed in copending application Ser. No. 379,108, filed May 17, 1982 to Plante et al. These detergent compositions are used as prewipe or precleaner to remove the undesirable sealant before the body is subjected to the sequential treatment prior to the application of a siccative coating. This sequential treatment comprises a cleaning step, a water rinse, application of a pre-coat (a phosphate coating), a water rinse, and drying. The pre-wipe or pre-cleaning with these detergent compositions not only removes the sealant, but also other undesirable materials and thus helps in preventing or delaying the contamination of the cleaner composition which is subsequently used.
These detergent compositions were found to be satisfactory in pre-treating automotive bodies which were constructed of steel. However, when the metal used in these bodies included sections of galvanized steel, problems appeared. This occurred, for example, when General Motors began the manufacture of the 1982 Citation hatch-back since this new hatch-back had an all ultra-smooth galvanized steel hatch-back lid; the rest of the body being formed of the type of steel previously used. Except for the hatch-back lid, very uniform precoats (i.e. phosphate coatings) were obtained on automobile bodies treated as described above; however, the phosphate coatings on the metal of the lid were streaky and covered with white spots. Good siccative coatings cannot be obtained on such streaky and spotted surfaces. Apparently, some component or components in these detergent compositions is reacting with the zinc in the galvanized steel thereby causing the undesirable streaking and spotting.
Accordingly, it is an object of this invention to provide a composition for the removal of undesired sealant from automobile bodies the use of which will not result in streaking or spotting on galvanized steel when a phosphate precoat is subsequently applied.
It is another object of this invention to provide a composition for the removal of undesired sealant from the surface of galvanized steel without affecting the surface of the steel.
Other objects will appear from the description which follows.